Conventional data storage tape drives employ various error correction and recovery methods to detect and correct data errors which, if left unresolved, would compromise the integrity of information read from or written to the magnetic tape media. Events which can lead to data errors include defects on the media, debris between the tape head and the media, and other conditions that interfere with head/media data transfer operations.
Error correction and recovery may be thought of as two distinct operations that are employed at different stages of error processing. Error correction is conventionally implemented using error correction coding (ECC) techniques in which host data to be placed on a tape medium is encoded in a well-defined structure by introducing data-dependent redundancy information. The presence of data errors is detected when the encoded structure is disturbed. The errors are corrected by making minimal alternations to reestablish the structure. ECC error correction is usually implemented “on-the-fly” as data is processed by the tape drive apparatus. Various encoding schemes are known in the art.
Error recovery occurs when ECC error correction is unable to correct data errors or when thresholds for allowable error correction are exceeded. The error recovery process may require stopping the tape and reprocessing a data block in which an error was detected. Typical error recovery procedures include tape refresh operations wherein a tape is wound to its end and brought back to the error recovery point, tape backhitch or “shoeshine” operations wherein a tape is drawn back and forth across the tape head, backward tape read operations, tape tension adjustment operations and tape servo adjustment operations, to name a few, which a drive might be capable of (although not all drives may be capable of performing all such error recovery procedures).
Basic tape “mapping” has been employed to summarize errors and performance parameters by physical tape location. The resulting map may be offloaded from the tape drive via a host interface command or as a subset of a product dump file; it may then be formatted for engineering analysis by the manufacturer of the drive. Such mapping has typically been designed to focus on visualizing the tape media quality and recording channel defects. However, with the increasing design sophistication required to accomplish ever increasing data densities on the tape, there is a corresponding increasing reliance on complex recoveries and optimization performed internally by microcode, some of which may not be visible and therefore not available for analysis.